Galvanized steel piping was commonly used until roughly 1950. This piping typically lasts 40-60 years. Where it is found today in single family homes, it is usually near the end of its life. The connections are normally threaded at connections. This is a where you will typically see rust first.
When the pipe corrodes, the rust accumulation inside the pipe chokes down the diameter of the pipe, resulting in poor water pressure. As rust builds up inside the pipe, a brownish color is often noted in the water when a faucet is turned on, especially after several days of inactivity. This rust in the water usually dissipates after a few seconds.